There are a number of drill sharpener machines available today, some of which can sharpen common twist drills to the like-new drill geometry. However, many of such machines require rather skilled operators, and others only approach standardized drill geometry.
U.S. patents directed to drill sharpener machines and attachments, such as twist drill chucks, include: U.S. Pat. No. 4,916,866, Bernard et al; U.S. Pat. No. 4,485,596, Bernard et al; U.S. Pat. No. 4,471,581, Bernard et al; and U.S. Pat. No. 4,001,975, Bernard et al.
It is a primary object of this invention to provide a super precision drill sharpener technology so advanced that the machine takes all guesswork and most of the operator involvement out of twist drill sharpening.
Historically, common twist drills have been a very standardized tool. The geometry at the cutting end was a standardized geometry, generally selected by the Metal Cutting Tool Institute as the best geometry for all general purpose drilling, and had an included point of 118.degree., a lip relief of 6.degree. to 18.degree. (depending on drill diameter), and a chisel edge accurate to within 0.004 inch with the axis of the drill. In recent years, many new drill point geometries have become commonly used for special and general purpose drilling. The most prominent variations of the standard 118.degree. point are the 118.degree. "S" or Spiral point, the 135.degree. split point, or a combination of the two. In addition, a higher degree of chisel edge accuracy, down to 0.002 inch, is becoming more common. These new points are being used more and more because of their superior cutting ability, self-centering characteristics and ability to produce more accurate holes. Currently, about 30% to 40% of all twist drills produced in the United States are made with one of these point variations. Drills with the traditional standard point geometry, or the other mentioned variations, are purchasable at hardware stores and industrial supply distributors by homeowners, hobbyists, auto mechanics, building tradesmen, millwrights and machinists.
Good-quality, high-speed, steel twist drills are expensive; for example, the average current list price for 1/8-inch size, with a traditional 118.degree. point, is about $0.60; for 5/16-inch size, about $1.75; and for 1/2-inch size, about $4.00. Drill prices with "special" drill points are usually double in cost. Yet, only a very small percentage of the twist drills purchased are ever resharpened, because it is very difficult for even a master machinist to resharpen the cutting lips by hand and produce the most efficient geometry. Generally, drills resharpened by hand remove material inefficiently, quickly become overheated, lose their sharpness and are soon scrapped.
For these reasons, thousands of small manufacturers scrap a number of twist drills per day at an estimated average cost of $2.00 per each drill. Such loss can amount to a hundred or more dollars per week per manufacturer.
The size of possibly not less than 95 percent of all twist drills manufactured and used is within the range of 1/16 inch and 1 inch in diameter, and within this range, there are 64 fractional-inch sizes, 26 letter sizes, 56 numeral sizes and 145 millimeter sizes, and one of the main objects of this invention is to provide a drill sharpener whereby all of these different sizes of drills, about 300 in all, can be handled by one super precision drill sharpener mechanism.